1. Field of the Invention
The present invention relates to a camshaft phaser having positive phase locking at one or more camshaft-to-crankshaft orientations.
2. Related Art
Camshaft phasers are a class of devices which allow the valve operating camshaft of a reciprocating internal combustion engine to be timed, or phased, with respect to the crankshaft of the engine. Phasers typically use locking mechanisms to maintain a selected position during engine operation. Although sliding pins have been used for this purpose in the past, the results produced by pins have generally not been amenable to desired flexibility in camshaft timing because it is difficult to drive locking pins between adjacent, relatively rotating components at high speeds, as is often the case during automotive engine operation.
Various attempts have been made to at least consider, and sometimes implement, improved structures for providing high speed locking of connecting pins. For example, receiving holes have been enlarged diametrically. Although this allows latching to occur at high speed, this accommodation comes at the expense of imprecision of locating the camshaft with respect to the crankshaft.
Another means for enhancing the high speed locking capability of a phaser has been to taper or chamfer the locking pin. Although this, too, promotes high speed locking, the ramp effect of the chamfering sometimes causes the pin to work its way out of the hole, thereby allowing the desired camshaft phasing to be lost. A third way of promoting lockup under high speed is to provide a hard stop or, in other words, to lock the drive sprocket with respect to the remaining portion of the device only when the sprocket has been pulled over to a position at which further rotation with respect to the camshaft is not possible. This situation is undesirable because it allows the camshaft timing to be changed with only one degree of freedom, without any chance for further timing changes. Moreover, the timing usually produced with this arrangement is often not optimal for starting the engine, which is unfortunate because start-up is an operating mode in which more control over camshaft timing is desirable. Finally, it has been proposed to increase the spring constant of a compression spring which functions to cause a locking pin to extend into its locked position. This, however, causes operational limitations of the resulting device because the hydraulic pressure needed to retract the pin is increased, thereby limiting the conditions in which re-phasing may occur.
It would be desirable to provide a configuration for a camshaft phaser allowing positive pin lockup at high speed, and at different phase angles of the camshaft with respect to the crankshaft.